TLR4 Signaling Pathway Research Articles

MiR-124 Reduced Neuroinflammation after Traumatic Brain Injury by Inhibiting TRAF6

Introduction: Neuroinflammation contributes to secondary injury after traumatic brain injury (TBI), which has been mainly mediated by the microglia. MiR-124 was reported to play an important role in the polarization of microglia by targeting TLR4 signaling pathway. However, the role and mechanism of miR-124 in neuroinflammation mediated by microglia after TBI is unclear. To clarify this, we performed this research. Methods: The expression of miR-124 was first measured by RT-PCR in the injured brain at 1/3/7 days post-TBI. Then, miR-124 mimics or inhibitors administration was used to interfere the expression of miR-124 at 24 h post-TBI. Subsequently, the microglia polarization markers were detected by RT-PCR, the expression of inflammatory cytokines was detected by ELISA, the expression of TLR4/MyD88/IRAK1/TRAF6/NF-κB was measured by WB, and the neurological deficit was evaluated by NSS and MWM test. At last, in vitro experiments were performed to explore the exact target molecule of miR-124 on TLR4 signaling pathway. Results: Animal research indicated that the expression of miR-124 was downregulated after TBI. Upregulation of miR-124 promoted the M2 polarization of microglia and inhibited the activity of TLR4 pathway, as well as reduced neuroinflammation and neurological deficit after TBI. In vitro experiments indicated that miR-124 promoted the M2 polarization of microglia and reduced neuroinflammation by inhibiting TRAF6. Conclusion: This study demonstrated that upregulation of miR-124 promoted the M2 polarization of microglia and reduced neuroinflammation after TBI by inhibiting TRAF6.

Betulonic acid regulates oviduct epithelial cell inflammation through the TLR4, MAPK, and JAK/STAT signalling pathways.

Infertility is a common disease among women of childbearing age and seriously endangers the reproductive health of human beings. We aimed to study the active effect and mechanism of betulonic acid (BTA) on tubal inflammatory infertility. An inflammatory model was established in isolated rat oviduct epithelial cells. Immunofluorescence of cytokeratin 18 was performed in cells. The therapeutic effect of BTA on cells was observed. Subsequently, we added JAK/STAT inhibitor AG490 and MAPK inhibitor U0126 and measured the levels of inflammatory factors via enzyme-linked immunosorbent assay and qRT-PCR. CCK-8 assay was applied to test cell proliferation, whereas flow cytometry was used to measure apoptosis. The levels of TLR4, IκBα, JAK1, JAK2, JAK3, Tyk2, STAT3, p38, ERK and the phosphorylation of p65 were determined by Western blotting. Betulonic acid inhibited the activation of TLR4 and NF-κB signalling pathways, and significantly downregulated IL-1β, IL-6, and TNF-α, with high doses being the most effective. Furthermore, high-dose BTA promoted the proliferation of oviduct epithelial cells and inhibited apoptosis. In addition, BTA inhibited the activation of JAK/STAT signalling pathway to perform effectively in oviduct epithelial cells inflammation. The addition of AG490 led to the inhibition of the JAK/STAT signalling pathway. BTA also inhibited the activation of MAPK signalling pathway in oviduct epithelial cells inflammation. Under U0126 treatment, the inhibition of proteins in MAPK pathway by BTA was weakened. Therefore, BTA inhibited the TLR, JAK/STAT and MAPK signalling pathways. Our study provided a new therapeutic strategy for infertility caused by oviduct inflammation.

The synergistic effect of epigallocatechin-3-gallate and quercetin co-loaded hydrogel beads on inflammatory bowel disease.

The synergistic effect of epigallocatechin-3-gallate (E) and quercetin (Q) enhances the therapeutic efficacy on related diseases; however, the instability and lower bioavailability of E and Q limited their application. Therefore, E and Q were co-encapsulated in hydrogel beads (H) with sodium alginate (SA) and soybean protein isolate (SPI) to improve their stability and bioavailability. The anti-inflammatory effect and molecular mechanism of action of E and Q co-loaded H in inflammatory bowel disease (IBD) were also investigated. The results showed that EQH-treated macrophages produced the lowest NO and TNF-α at 18.64 μmol L-1 and 5855.25 ng mL-1, respectively. The protein expression of p-NF κB-p65 was the lowest in EQH, indicating that EQH inhibits the activation of the pro-inflammatory NF-κB signaling pathway. The colon length of IBD model rats fed EH, QH, and EQH increased; histological analysis revealed intact layers of colonic epithelial cells with no observable tissue damage. The TNF-α and IL-1β levels in the plasma of the EQH-treated rats decreased, indicating the inhibition of the TLR4 and NF-κB signaling pathways, and Q's level in the colon was the highest at 0.04 mg mL-1. This study provides a theoretical basis for the application of E and Q in IBD.

Tryptophol Acetate and Tyrosol Acetate, Small-Molecule Metabolites Identified in a Probiotic Mixture, Inhibit Hyperinflammation

Probiotic fermented foods are perceived as contributing to human health; however, solid evidence for their presumptive therapeutic systemic benefits is generally lacking. Here we report that tryptophol acetate and tyrosol acetate, small-molecule metabolites secreted by the probiotic milk-fermented yeast Kluyveromyces marxianus, inhibit hyperinflammation (e.g., “cytokine storm”). Comprehensive in vivo and in vitro analyses, employing LPS-induced hyperinflammation models, reveal dramatic effects of the molecules, added in tandem, on mice morbidity, laboratory parameters, and mortality. Specifically, we observed attenuated levels of the proinflammatory cytokines IL-6, IL-1α, IL-1β, and TNF-α and reduced reactive oxygen species. Importantly, tryptophol acetate and tyrosol acetate did not completely suppress proinflammatory cytokine generation, rather brought their concentrations back to baseline levels, thus maintaining core immune functions, including phagocytosis. The anti-inflammatory effects of tryptophol acetate and tyrosol acetate were mediated through downregulation of TLR4, IL-1R, and TNFR signaling pathways and increased A20 expression, leading to NF-kB inhibition. Overall, this work illuminates phenomenological and molecular details underscoring anti-inflammatory properties of small molecules identified in a probiotic mixture, pointing to potential therapeutic avenues against severe inflammation.

Resveratrol Attenuates Heat-Stress-Impaired Immune and Inflammatory Responses of Broilers by Modulating Toll-Like Receptor-4 Signaling Pathway

This study investigated the effect of resveratrol on the immune and inflammatory responses and the mRNA levels of splenic toll-like receptor (TLR)-4 signaling pathway-related genes of broilers under heat stress (HS). One hundred and sixty-two birds were allocated to three groups, each with 6 replicates, for 21 continuous days. The three treatments were as follows: the control group (22 ± 1 °C), the HS (33 ± 1 °C for 10 h d-1 and 22 ± 1 °C for the remaining time) group and the HS + resveratrol (400 mg kg-1) group. At the end of the trial, one bird per replicate close to the average body weight (BW) was selected, exsanguinated, and slaughtered. Compared with the control group, the HS treatment decreased (p<0.05) final BW, average daily gain (ADG), average daily feed intake (ADFI), relative weight of bursa of Fabricius and spleen, serum immunoglobulin (Ig) Y, IgA and interleukin (IL)-10 contents, and splenic IL-10 mRNA level, while it increased (p<0.05) feed/gain, mRNA levels of splenic tumor necrosis factor-α (TNF-α), TLR-4, nuclear factor-kappa-B (NF-κB), IL-1β, and IL-6. Compared to the HS group, the HS+resveratrol group exhibited increased (p<0.05) final BW, ADG, relative weight of bursa of Fabricius and spleen, serum IgY, IgA and IL-10 contents, and splenic IL-10 mRNA level, while it exhibited lower (p<0.05) TNF-α, IL-1β and IL-6 contents in serum, and splenic TLR4, TNF-α, IL-1β, and NF-κB mRNA levels. In conclusion, resveratrol prevented a HS-impairment of the immune function of broilers by blocking the abnormal activation of the TLR4 signaling pathway.

Intracellular osteopontin protects from autoimmunity-driven lymphoma development inhibiting TLR9-MYD88-STAT3 signaling

BackgroundAutoimmune disorders, including Systemic Lupus Erythematosus (SLE), are associated with increased incidence of hematological malignancies. The matricellular protein osteopontin (OPN) has been linked to SLE pathogenesis, as SLE patients show increased serum levels of OPN and often polymorphisms in its gene. Although widely studied for its pro-tumorigenic role in different solid tumours, the role of OPN in autoimmunity-driven lymphomagenesis has not been investigated yet.MethodsTo test the role of OPN in the SLE-associated lymphomagenesis, the SLE-like prone Faslpr/lpr mutation was transferred onto an OPN-deficient background. Spleen from Faslpr/lpr and OPN-/-Faslpr/lpr mice, as well as purified B cells, were analysed by histopathology, flow cytometry, Western Blot, immunohistochemistry, immunofluorescence and gene expression profile to define lymphoma characteristics and investigate the molecular mechanisms behind the observed phenotype. OPN cellular localization in primary splenic B cells and mouse and human DLBCL cell lines was assessed by confocal microscopy. Finally, gain of function experiments, by stable over-expression of the secreted (sOPN) and intracellular OPN (iOPN) in OPN-/-Faslpr/lpr -derived DLBCL cell lines, were performed for further validation experiments.ResultsDespite reduced autoimmunity signs, OPN-/-Faslpr/lpr mice developed splenic lymphomas with higher incidence than Faslpr/lpr counterparts. In situ and ex vivo analysis featured such tumours as activated type of diffuse large B cell lymphoma (ABC-DLBCL), expressing BCL2 and c-MYC, but not BCL6, with activated STAT3 signaling. OPN-/-Faslpr/lpr B lymphocytes showed an enhanced TLR9-MYD88 signaling pathway, either at baseline or after stimulation with CpG oligonucleotides, which mimic dsDNA circulating in autoimmune conditions. B cells from Faslpr/lpr mice were found to express the intracellular form of OPN. Accordingly, gene transfer-mediated re-expression of iOPN, but not of its secreted isoform, into ABC-DLBCL cell lines established from OPN-/-Faslpr/lpr mice, prevented CpG-mediated activation of STAT3, suggesting that the intracellular form of OPN may represent a brake to TLR9 signaling pathway activation.ConclusionThese data indicate that, in the setting of SLE-like syndrome in which double strand-DNA chronically circulates and activates TLRs, B cell intracellular OPN exerts a protective role in autoimmunity-driven DLBCL development, mainly acting as a brake in the TLR9-MYD88-STAT3 signaling pathway.

Extracellular traps from activated vascular smooth muscle cells drive the progression of atherosclerosis

Extracellular DNA traps (ETs) represent an immune response by which cells release essential materials like chromatin and granular proteins. Previous studies have demonstrated that the transdifferentiation of vascular smooth muscle cells (VSMCs) plays a crucial role in atherosclerosis. This study seeks to investigate the interaction between CD68+ VSMCs and the formation of ETs and highlight its function in atherosclerosis. Here we show that ETs are inhibited, and atherosclerotic plaque formation is alleviated in male Myh11CrePad4flox/flox mice undergoing an adeno-associated-virus-8 (AAV8) mediating overexpression of proprotein convertase subtilisin/kexin type 9 mutation (PCSK9) injection and being challenged with a high-fat diet. Obvious ETs generated from CD68+ VSMCs are inhibited by Cl-amidine and DNase I in vitro. By utilizing VSMCs-lineage tracing technology and single-cell RNA sequencing (scRNA-seq), we demonstrate that the ETs from CD68+ VSMCs influence the progress of atherosclerosis by regulating the direction of VSMCs’ transdifferentiation through STING-SOCS1 or TLR4 signaling pathway.

RNA-seq analysis of a zebrafish caudal fin cell line in response to infection with spring viraemia of carp virus

A cell line, termed ZFIN, was established from the caudal fin of zebrafish and was shown to be susceptible to spring viremia of carp virus (SVCV). The ZFIN cells are epithelial like cells and have a moderate plasmid transfection efficiency of 13.9%. Using an RNA-seq approach, differentially expressed genes (DEGs) regulated by SVCV were identified. Infection of SVCV gave rise to 3931 DEGs and up-regulated DEGs were mostly enriched into the biological regulation and cellular processes, among which pathways for the type I interferon signaling and the response to exogenous dsRNA were the top two GO terms. Several KEGG signaling pathways including TLR signaling pathway, RLR receptor signaling pathway, cytosolic DNA-sensing pathway, NLR signaling pathway, cytokine-cytokine receptor interaction and ferroptosis were significantly enriched. Antiviral genes including ifnφ1, isg15 and mx were significantly up-regulated. In addition, key DEGs involved in autophagy were identified. The results indicate that the ZFIN cell line provides a useful in vitro tool for study on the gene functions and cellular responses to viral infection in fish.

Butyrate impeded the conscription of MDSCs to reduce CAC formation by blocking the TLR2 signaling pathway

• Butyrate alleviated CAC development. • Butyrate inhibited proliferation and promoted apoptosis of CAC cells. • Butyrate inhibited the levels of MDSCs and cytokine in the TME. • Butyrate inhibited the activation of TLR2 signaling pathway. • Butyrate inhibited DSS-induced inflammation by TLR2 in Caco-2 cells. This study focuses on how butyrate alleviates CAC simulated by AOM-DSS through TLR2 signals and MDSCs, which is still unclear. Our results revealed that butyrate slowed tumorigenesis supported by remission of weight loss, survival index, DAI, pathological dysplasia, the number and size of tumors. Butyrate caused a reduction of proinflammatory factors such as IL-12, IL-6, and TNF-α as well as MDSCs that help tumor immune escape in TME. The up-regulation of TLR2/Myd88/ NF-κB in intestinal tissues of CAC was also significantly inhibited by butyrate. Besides, the inhibition of butyrate on the up -regulation of TLR2 caused by TLR2 agonist Pam3csk4 and DSS inflammatory injury in Caco-2 cells fully proved its anti-inflammatory effect through TLR2 signal pathway. So, the above results implied that by suppressing TLR2 signals, butyrate may decrease the production of IL-6, IL-12, and TNF-α to restrict the MDSCs conscription in TME and halt the CAC progression.

Evaluation and mechanism of immune enhancement effects of Pleurotus ferulae polysaccharides-gold nanoparticles

We previously demonstrated that Pleurotus ferulae polysaccharide (PFPS) promoted dendritic cell (DC) maturation through the TLR4 signaling pathway. To improve PFPS activity and bioavailability, gold nanoparticles with PFPS (PFPS-Au NPs) were synthesized. Of note, although the polysaccharide content of PFPS-Au NPs was only one tenth of PFPS, PFPS-Au NPs enhanced the immunostimulatory activities of PFPS in the maturation and function of dendritic cells (DCs) by TLR4 and NLRP3 signaling pathways, evidenced by stronger activation of the down-stream MAPK and NF-κB pathways and NLRP3 inflammasome pathway. More importantly, PFPS-Au NPs enhanced DC migration and murine immunity, particularly in type 1 T-helper cell responses. Moreover, the half-life of PFPS-Au NPs (2.217 ± 0.187 h) was longer than that of PFPS (1.39 ± 0.257 h) in the blood and the distribution of PFPS-Au NPs (19.8 %) in the spleen was significantly increased compared with PFPS (13.3 %), indicating the improved bioavailability in vivo. PFPS-Au NPs as an adjuvant promoted antigen-specific cellular immune responses to an HPV DC-based vaccine, which significantly inhibited the growth of TC-1 tumors in mice. All results suggest that the prepared Au NPs could enhance PFPS-immunostimulatory activity, which will pave the way for PFPS-Au NPs to be applied in clinical trials.

Analysis of Macrophage Chemotactic Activity and TLR9 Signaling Pathway in the Mouse Model of Viral Acute Lung Injury.

This study focused on the chemotactic activity of macrophages and the role of the TLR9 signaling pathway in the pathogenesis of viral Acute Lung Injury (ALI). For this purpose, a total of 40 male SPF mice were used, aged 5-8 weeks. They were randomly divided into an experimental group and a control group. The experimental group was further divided into S1 and S2, and the control group was further divided into D1 and D2, with 10 in each. The different groups were detected for the expression of inflammatory cytokines and chemokines and the expression of alveolar macrophages. Results showed that as for the weight, survival status, arterial blood gas analysis, lung index and wet-to-dry value of lung tissue, and lung histopathological analysis results, the S2 group showed more obvious changes versus the D2 group, and the difference was statistically significant (P<0.05). S2 had higher levels of the inflammatory factors TNF-α, IL-1β, IL-6 and the chemokine CCL3 in the BALF supernatant versus the D2 Group, and the difference is statistically significant (P<0.05). S2 had higher expression levels of chemokines CCR5, TLR9, and JMJD1A mRNA versus the D2 group, and the difference was statistically significant (P<0.05). In conclusion, the establishment of a mouse ALI model induced by poly l:C was successful; AM has a certain chemotactic activity on CCL3; polyI:C can promote the expression activity and chemotactic activity of macrophages CCR5 through signal pathways, such as TLR9.

Keratinocyte TLR2 and TLR7 contribute to chronic itch through pruritic cytokines and chemokines in mice.

Although neuronal Toll-like receptors (TLRs) (e.g.,TLR2, TLR3, and TLR7) have been implicated in itch sensation, the roles of keratinocyte TLRs in chronic itch are elusive. Herein, we evaluated the roles of keratinocyte TLR2 and TLR7 in chronic itch under dry skin and psoriasis conditions, which was induced by either acetone-ether-water treatment or 5% imiquimod cream in mice, respectively. We found that TLR2 and TLR7 signaling were significantly upregulated in dry skin and psoriatic skin in mice. Chronic itch and epidermal hyperplasia induced by dry skin or psoriasis were comparably reduced in TLR2 and TLR7 knockout mice. In the dry skin model, the enhanced messenger RNA(mRNA) expression levels of pruritic CXCL1/2, IL-31, IL-33, ST2, IL-6, IL-17A, TNF-α, and IFN-γ were inhibited in TLR2-/- mice, while CXCL2, IL-31, and IL-6 were inhibited in TLR7-/- mice. In psoriasis model, the enhanced mRNA expression levels of pruritic CXCL1/2, IL-31, IL-33, ST2, IL-6, and TNF-α were inhibited in TLR2-/- mice, while CXCL1/2, IL-31, IL-33, ST2, IL-6, IL-17A, and TNF-α were inhibited in TLR7-/- mice. Incubation with Staphylococcus aureus (S. aureus) peptidoglycan (PGN-SA) (a TLR2 agonist), imiquimod (a TLR7 agonist), and miR142-3p (a putative TLR7 agonist) were sufficient to upregulate the expression of pruritic cytokines or chemokines in cultured keratinocyte HaCaT cells. Finally, pharmacological blockade of C-X-C Motif Chemokine Receptor 1/2 and high mobility group box protein 1 dose-dependently attenuated acute and chronic itch in mice. Together, these results indicate that keratinocyte TLR2 and TLR7 signaling pathways are distinctly involved in the pathogenesis of chronic itch.

Immunomodulatory Effect of Lactobacillus reuteri (Limosilactobacillus reuteri) and Its Exopolysaccharides Investigated on Epithelial Cell Line IPEC-J2 Challenged with Salmonella Typhimurium.

The gastrointestinal tract is the largest and most complex component of the immune system. Each component influences the production and regulation of cytokines secreted by intestinal epithelial cells. The aim of this study was to see how the probiotic strain Limosilactobacillus reuteri L26 and its exopolysaccharide (EPS) affect porcine intestinal-epithelial cells IPEC-J2 infected with Salmonella Typhimurium. The results revealed that Salmonella infection up-regulated all studied pro-inflammatory cytokines such as TNF-α, IL-8, IL-6 and TLR4, TLR5 signaling pathways, while decreasing the expression of TGF-β. An immunosuppressive activity was found in EPS-treated wells, since the transcriptional levels of the studied pro-inflammatory cytokines were not increased, and the pretreatment with EPS was even able to attenuate up-regulated pro-inflammatory genes induced by Salmonella infection. However, there was a significant increase in the expression of mRNA levels of IL-8 and TNF-α in L26-treated cells, although this up-regulation was suppressed in the case of pretreatment. The immunoregulatory function of L. reuteri was also confirmed by the increased level of mRNA expression for TGF-β, a known immunosuppressive mediator. The most relevant finding of this ex vivo study was a case of immunity modulation, where the probiotic strain L. reuteri stimulated the innate immune-cell response which displayed both anti- and pro-inflammatory activities, and modulated the expression of TLRs in the IPEC-J2 cell line. Our findings also revealed that the pretreatment of cells with either EPS or live lactobacilli prior to infection has a suppressive effect on the inflammatory response induced by Salmonella Typhimurium.

Anti-CD70 Monoclonal Antibodies Show Efficacy in Preclinical Models for Chronic Lymphoblastic Leukemia

Although therapy for chronic lymphocytic leukemia (CLL) has improved significantly with combination therapies that include ibrutinib and/or anti-B cell mAbs, resistance can develop, and patients can discontinue therapy for various reasons. Therefore, effective, alternative therapies are needed. CD70, a TNF family member, and its receptor, CD27, are mainly expressed on B and T lymphocytes. Different from normal B cells that only transiently express CD70 upon activation, CLL B cells stably express the molecule at relatively high levels, suggesting a fundamental biologic abnormality and adding another example of the dysregulation of the immune system in CLL. Here we investigated the role of CD70 in CLL using blocking anti-CD70 mAbs in preclinical mouse models of the disease. We first confirmed stable expression of CD27 and CD70 in patient samples as well as on murine TCL1 CLL B cells, including TCL1-192 cells, a set of primary murine leukemic cells within which > 95% cells react to autoantigen stimulation via the B-cell receptor (BCR). Comparing with healthy BM, we found that primary CLL patient B cells express significantly higher levels of the CD27 - CD70 receptor-ligand pair at both mRNA and protein levels, as do TCL-1 mice. We next investigated the effects of an anti-mouse CD70 effector function silenced/blocking mAb, FcD-FR70, on TCL1-192 CLL cells in vitro and in vivo in preclinical models. In vitro, treating TCL1 CLL cells with FcD-FR70 significantly inhibited CD40L-induced CLL cell growth. In vivo, twice weekly 10 mg/kg treatments with FcD-FR70 antibody significantly reduced the number of murine CLL B cells in spleens, lymph nodes and blood. The levels of reduction were comparable to those observed in anti-CD19 mAb or ibrutinib treated mice. There was a significantly better treatment outcome when therapy was initiated earlier. Moreover, the level of soluble mouse CD27, the product of CD27 cleavage after interaction with CD70, was significantly reduced in sera of animals treated with FcD-FR70. Notably, FcD-FR70, but not anti-CD19 mAb or ibrutinib, significantly reduced CD70 membrane levels. CD27 expression levels were not altered by all treatments. As CD27 and CD70 are inversely expressed in B cells, due to tight control at the transcriptional and posttranslational levels, this result strongly suggests preferential depletion of malignant cells with the high CD70 expression, which also affects levels of soluble CD27. We then performed bulk RNAseq analysis in CD19+CD5+ splenic cells from mice treated with control or FcD-FR70 antibody. Genes differing by >1.5 fold (P < 0.01) by FcD-FR70 treatment between the two groups included upregulated cell cycle regulator cyren and interferon gamma inducible protein IfI211, as well as downregulated IL10, CCR7, PIM3, PIM1, TGFb3, TNFaip3, JunB and CD69. Importantly, IPA analysis of the altered genes suggested inhibition of TLR7, TLR9, TNF, NFKB, IL4, BCR, BTK, and CD40L signaling pathways. Thus, FcD-FR70 treatment blocked key survival pathways, inducing death of CLL B cells. Finally, we studied the effect of anti-CD70 antibodies on CLL B-T cell interactions. Adding the FcD-FR70 mAb to an allo-MLR significantly blocked T cell proliferation and survival induced by TCL1-192 leukemic B cells (P < 0.01). We then tested the effects of 41D12-FcD, a blocking mAb in human IgG1 format that binds with picomolar affinity to human CD70, in a primary CLL patient derived xenograft model. This revealed a significant reduction of malignant cells in the spleen, BM, and peritoneum (P < 0.001). Interestingly, the efficacy of the blocking 41D12-FcD antibody was associated with a significant decrease of human T cells, suggesting that the antibody directly blocked the proliferation of malignant B cells and also inhibited T cell-CLL cell interactions. Notably, no significant changes were seen in the differentiation of T cells, expression of CTLA4, PD1, PD-L1, and levels of Th1/Th2 cytokines after anti-CD70 treatment. Overall, data from our preclinical models suggest targeting CD70 in CLL alters BCR, CD40L, IL4, and TNF receptor signaling and delays CLL disease progression. Although the involvement of CD70 and the relationships between CLL B cells and non-malignant cells needs further study, the availability of clinical stage therapeutic anti-CD70 antibodies supports the use anti-CD70 immunotherapy in combination therapies in CLL.

Heme and Iron Aggravate Tissue Damage in Sickle Cell Disease By Driving Macrophage Functional Reprogramming through the Coordinated Suppression of Efferocytosis and Mitochondrial Metabolism

Introduction: Sickle cell disease (SCD) is hallmarked by an underlying chronic inflammatory status, which is in part driven by pro-inflammatory macrophages. Macrophages are highly plastic immune cells which integrate and respond to a variety of signals they are exposed to in the surrounding microenvironment. One of these stimuli is represented by heme released upon hemolysis, which acts as damage-associated molecular pattern to stimulate macrophage inflammatory phenotypic switching through TLR4 signaling and ROS production (Vinchi et al., Blood 2016). Heme-induced pro-inflammatory activation program in macrophages promotes sterile inflammation and aggravates hepatic fibrosis in SCD, contributing to the inflammatory landscape and organ damage typically associated with this disease. While previous studies addressed heme ability to induce inflammatory cytokine production in macrophages, how heme alters cell functional properties remains unexplored. Macrophage functions such as immune cell recruitment ability and apoptotic cell clearance are relevant in the context of SCD, where tissue damage and cell apoptosis occur frequently due to vaso-occlusive episodes, hypoxia and ischemic injury. Methods: Here we analyzed macrophage response to apoptotic stimuli in vivo, in mouse models of heme overload and SCD, as well as in vitro, in bone-marrow-derived macrophages (BMDMs), to unveil the impact of hemolysis on macrophage functional properties. Results: Our results demonstrate that, in addition to inflammatory activation, heme severely alters macrophage functional response to apoptotic cell damage by exacerbating their immune cell recruitment ability and impairing their efferocytic capacity. We show that exposure to heme excess drives defective efferocytosis of apoptotic neutrophils in BMDMs and mouse model of heme overload. This is fully recapitulated in SCD mice, where limited efferocytosis contributes to impaired apoptotic cell clearance and exacerbated tissue damage. Mechanistically, altered efferocytosis depends on heme-driven activation of TLR4 signaling pathway and the suppression of the nuclear transcription factor PPARγ and its coactivator PGC1α, which lead to reduced expression of efferocytic receptors and impaired mitochondrial dynamics and functions. This results in limited recognition/engulfment of apoptotic cells and decreased shift to aerobic mitochondrial fatty acid β-oxidation and anti-inflammatory IL-4 and IL-10 release, with consequent inhibition of continual efferocytosis, inflammation resolution and tissue repair. Heme-driven changes are associated with cell metabolic skewing towards glycolysis and pentose phosphate pathway and reduced reliance on mitochondrial fatty acid oxidation and TCA cycle. Macrophages pre-loaded with fatty acids showed decreased oxygen consumption rate and ATP production after heme exposure, indicating that heme-altered mitochondrial dynamics impair lipid catabolism via limited mitochondrial oxidative phosphorylation. Overall, heme induces macrophage phenotypic and functional reprogramming through the coordinated suppression of efferocytosis, via efferocytosis receptor downregulation, and fatty acid β-oxidation, via altered mitochondrial dynamics. We further demonstrate that heme-impaired efferocytosis and tissue damage promote autoimmunity through anti-nuclear antibody production against 'self' secondary necrotic cells, potentially explaining the increasing evidence of autoimmune diseases in SCD patients. Finally, hemopexin-mediated heme scavenging and anti-inflammatory IL-4 treatment improve tissue damage in hemolytic mice through macrophage rewiring. Defective efferocytosis is reproduced in vitro by macrophage exposure to SCD patients' plasma and rescued by heme scavenging via haptoglobin/hemopexin and PPARγ/PGC1α modulation via PPARα agonist or IL-4. Conclusion: Our data indicate that the therapeutic improvement of heme-altered macrophage functional properties via heme scavenging or PPARγ/PGC1α modulation significantly promotes the resolution of inflammation and ameliorates tissue damage associated with SCD pathophysiology. Thus, macrophage functional rewiring offers potentially valuable therapeutic strategies for SCD patients to improve tissue damage resolution upon vaso-occlusive crisis and ischemic events and prevent autoimmune conditions.

Neuroprotective Effects of Nicotinamide against MPTP-Induced Parkinson's Disease in Mice: Impact on Oxidative Stress, Neuroinflammation, Nrf2/HO-1 and TLR4 Signaling Pathways.

Nicotinamide (NAM) is the amide form of niacin and an important precursor of nicotinamide adenine dinucleotide (NAD), which is needed for energy metabolism and cellular functions. Additionally, it has shown neuroprotective properties in several neurodegenerative diseases. Herein, we sought to investigate the potential protective mechanisms of NAM in an intraperitoneal (i.p) 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease (PD) mouse model (wild-type mice (C57BL/6N), eight weeks old, average body weight 25-30 g). The study had four groups (n = 10 per group): control, MPTP (30 mg/kg i.p. for 5 days), MPTP treated with NAM (500 mg/kg, i.p for 10 days) and control treated with NAM. Our study showed that MPTP increased the expression of α-synuclein 2.5-fold, decreased tyrosine hydroxylase (TH) 0.5-fold and dopamine transporters (DAT) levels up to 0.5-fold in the striatum and substantia nigra pars compacta (SNpc), and impaired motor function. However, NAM treatment significantly reversed these PD-like pathologies. Furthermore, NAM treatment reduced oxidative stress by increasing the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) between 0.5- and 1.0-fold. Lastly, NAM treatment regulated neuroinflammation by reducing Toll-like receptor 4 (TLR-4), phosphorylated nuclear factor-κB, tumor (p-NFκB), and cyclooxygenase-2 (COX-2) levels by 0.5- to 2-fold in the PD mouse brain. Overall, these findings suggest that NAM exhibits neuroprotective properties and may be an effective therapeutic agent for PD.

Treponema pallidum FlaA2 inducing the release of pro-inflammatory cytokines is mediated via TLR2 in keratinocytes

BackgroundSyphilis, caused by Treponema pallidum (T. pallidum), is a multi-organ, multiple systems, multi-stage sexually transmitted diseases with various clinical manifestations, among of which pathological lesions of skin and mucosa are the typical clinical manifestations of syphilis. However, the immunopathogenesis of this process is poorly understood. T. pallidum flagellin FlaA2, as a part of the important organelle responsible for the causative agent's motility, may contributes to the host skin inflammatory response. ObjectivesTo determine the mechanisms of T. pallidum FlaA2 stimulating the expression of pro-inflammatory cytokines in human keratinocytes. MethodsRecombinant FlaA2 protein was performed to stimulate human keratinocytes. The mRNA transcription levels and protein expression levels of IL-6 and IL-8 were detected by qRT-PCR and ELISA, respectively. Western blot was used to detect the total protein and phosphorylation levels of ERK, p38, JNK and NF-κB, respectively. The intracellular location of NF-κB p65 was detected by immunofluorescence staining. ResultsRecombinant FlaA2 could considerably induced the expression of pro-inflammation cytokines IL-6 and IL-8 in HaCaT cells, and FlaA2-induced IL-6 and IL-8 secretion could be decreased by inhibiting TLR2 using pZERO-hTLR2. Further investigation showed that FlaA2 could activate the phosphorylation of ERK, p38 and IκBα and FlaA2-stimulated secretion of IL-6, IL-8 were attenuated by ERK, p38 and NF-κB inhibitors in HaCaT cells. Moreover, FlaA2 activates the ERK, p38 and NF-κB pathways through TLR2 signaling pathway in HaCaT cells. ConclusionsFrom the findings above, these results confirm that T. pallidum FlaA2 activates ERK, p38 and NF-κB signaling pathway through TLR2 pathway to induce the production of IL-6 and IL-8, which could contribute to enhance the understanding of the skin inflammatory response induced by the pathogen in syphilis patients.

Glycyrrhizin Interacts with TLR4 and TLR9 to Resolve P. aeruginosa Keratitis.

This study tests the mechanism(s) of glycyrrhizin (GLY) protection against P. aeruginosa keratitis. Female C57BL/6 (B6), TLR4 knockout (TLR4KO), myeloid specific TLR4KO (mTLR4KO), their wildtype (WT) littermates, and TLR9 knockout (TLR9KO) mice were infected with P. aeruginosa KEI 1025 and treated with GLY or PBS onto the cornea after infection. Clinical scores, photography with a slit lamp, RT-PCR and ELISA were used. GLY effects on macrophages (Mϕ) and polymorphonuclear neutrophils (PMN) isolated from WT and mTLR4KO and challenged with KEI 1025 were also tested. Comparing B6 and TLR4KO, GLY treatment reduced clinical scores and improved disease outcome after infection and decreased mRNA expression levels in cornea for TLR4, HMGB1, and RAGE in B6 mice. TLR9 mRNA expression was significantly reduced by GLY in both mouse strains after infection. GLY also significantly reduced HMGB1 (B6 only) and TLR9 protein (both B6 and TLR4KO). In TLR9KO mice, GLY did not significantly reduce clinical scores and only slightly improved disease outcome after infection. In these mice, GLY significantly reduced TLR4, but not HMGB1 or RAGE mRNA expression levels after infection. In contrast, in the mTLR4KO and their WT littermates, GLY significantly reduced corneal disease, TLR4, TLR9, HMGB1, and RAGE corneal mRNA expression after infection. GLY also significantly reduced TLR9 and HMGB1 corneal protein levels in both WT and mTLR4KO mice. In vitro, GLY significantly lowered mRNA expression levels for TLR9 in both Mϕ and PMN isolated from mTLR4KO or WT mice after incubation with KEI 1025. In conclusion, we provide evidence to show that GLY mediates its effects by blocking TLR4 and TLR9 signaling pathways and both are required to protect against disease.

Expression of Concern: miR-26a-5p mediates TLR signaling pathway by targeting CTGF in LPS induced alveolar macrophage.

The Editorial Office has been made aware of potential issues surrounding the scientific validity of this paper, hence has issued an expression of concern to notify readers whilst the Editorial Office investigates. It has been noted that the ‘Model’ line in the flow cytometry data from Figure 5B would be impossible to attain, as it should not bend to the left in such a way when the X value is increasing

Antinociceptive effect of ultra-low dose naltrexone in a pre-clinical model of postoperative orofacial pain

Painmanagement after oral surgeries is essential to enhance recovery, reduce negative outcomes and improve the experience of the patient. Naltrexone (NTX) is a non-selective opioid receptor antagonist that has been shown to modulate neuro-inflammation when employed in low to ultra-low doses. In addition, ultra-low dose naltrexone (ULDN) has been shown to potentiate opioids’ analgesia and to have opioid-sparing effects. Herein it was investigated the effect of ULDN in a model of postoperative orofacial pain in rats, and it was tested the hypothesis that blockade of TLR4-signalling pathway contributes to its antinociceptive effect. Systemic NTX reduced heat hyperalgesia in female rats and heat and mechanical hyperalgesia in male rats after incision surgery. Combined treatment with NTX and morphine, both at ineffective doses, resulted in a significant reduction of heat hyperalgesia in male rats. NTX injection at the incision site failed to change heat hyperalgesia, but injection at the trigeminal ganglion (TG) or subnucleus caudalis (Sp5C) caused a significant reduction in heat hyperalgesia. At these sites, blockade of TLR4 impeded NTX effect. Lipopolysaccharide (LPS) injection in the intraoral mucosa resulted in facial heat hyperalgesia an increase in IL-1β levels in the TG, which were reduced by systemic NTX. Stimulation of macrophages with LPS resulted in increase of nitric oxide, IL-1β and CXCL-2 levels which were reduced by NTX. Altogether, these results provide evidence for an antinociceptive effect of ULDN in postoperative orofacial pain and suggest that blockade of TLR4 and downstream signaling pathway contribute to its effect.